LAND CRUSTACEANS. 81 



a series of small transverse ridges, and each of these is again made up of a row of four 

 or five minute oval beads set with their long axes lengthways in the intestine, that is 

 transversely to the ridge which each row of them composes. The whole of these structures 

 are, of course, covered with a delicate chitinous pellicle. In the anterior region of the 

 hind-gut, where the ridges are wanting, the inner surface is covered with similar small 

 beads, less regular in shape, set in longitudinal rows. The transition from the mid- to the 

 hind-gut is hardly visible outwardly in fresh specimens, but in a gut which has been for 

 a few hours in spirit it is very easy to see, owing to the difference in calibre brought 

 about by the shrinkage of the mid-gut. Internally, the beaded appearance of the hind-gut 

 makes the distinction a sharp one. In the natural position of the organs in the body a 

 great part of the hind-gut is hidden by the overlapping lobules of the liver, but more 

 or less of the hinder part usually comes into sight amongst the lobules. 



The anus (fig. IS) is situated on the under side of the telsou. It is guarded by a 

 strong valve in the form of an oval calcified convex plate (1, fig. 18), attached to the soft 

 ventral wall of the telson in front of the anus, and projecting back under it. If this 

 plate be parted from the body of the telson, the anus is seen as a longitudinal slit at 

 the bottom of the hollow between it and the telson. Between these two structures, then, 

 there is a sort of cloaca, into which the anus opens. The aperture of the cloaca is surrounded 

 by a thick growth of hairs. The result of this arrangement is that the opening for the 

 discharge of faeces is directed, not ventralwards, in which case it would be liable to be 

 pressed against the columella of the shell and thus obstructed, but backwards, and is 

 further protected from pressure by the stout plate beneath it. Possibly the object of the 

 hairs round the opening is to prevent the entrance of faecal matter as the animal shifts 

 in its .shell, though it is remarkable that the shells of these voracious creatures contain 

 quite a small quantity of dung. In the Galatheinea and Brachyura, groups whose members 

 carry the abdomen pressed more or less strongly against the underside of the thorax, the 

 same arrangement is found in a less complete form, the anus being usually prominent and 

 directed more or less backwards. 



(iii) The vascular system (fig. 19). 



The rather large, muscular heart (19, fig. 19) lies, as usual in the thorax, close under 

 the dorsal carapace behind the cervical groove, surrounded by the thin-walled pericardial sinus, 

 in which it is suspended by the three pairs of fibrous alae cordis, and with which it 

 communicates by the usual three pairs of ostia. In shape it appears roughly four-sided 

 from above, the anterior end being drawn out into a low prominence from which arise the 

 three anterior arteries. The hind end has also a low, rounded, median bulge. At about 

 a third of its length from the hind end there is on each side a notch. The dorsal .surface 

 is slightly convex ; the sides slope inwards to the ventral surface, which is flat, and is raised, 

 at the hind end, into a round, median lobe, from which the sternal and abdominal arteries 

 arise. 



Arteries. Seven vessels are given off from the heart. At the front end there arises 

 a group of three — a median ophthalmic and two lateral antennaries. A short distance behind 

 these the paired hepatics are given off from the ventral surface of the heart ; and at the 

 hind end the ventral lobe bears two median arteries, a more anterior, ventrally directed 

 sternal, and a more posterior, terminal abdominal. 



G. 11 



